In vivo systems for studying vascular development and arteriogenesis are inherently complex. In vivo, vascular cells involved in arteriogenesis and vascular remodeling experience many simultaneous stimuli that are difficult to control, including shear stress, stretch, oxygen levels, growth factors and substrate cues. In addition, in vivo systems are typically assessed in destructive ways - animals must often be sacrificed in order to gain a window onto arteriogeneic processes. Therefore, studying vascular development in vivo is time consuming, expensive, and subject to many factors that cannot be experimentally controlled. Conversely, standard cell culture systems are convenient, inexpensive and can be monitored nondestructively. However, simple 2-D cultures cannot replicate the complex shear stress and substrate environments that are present during in vivo arteriogenesis. For these reasons, we have developed novel culture systems that bridge the gap between these two existing methods. Our novel bioreactors allow the systematic control of cell type, substrate composition, soluble factors, and physical forces such as radial strain and shear stress. Hence, these bioreactors enable the control of many of the factors that are involved in vessel formation in vivo, but that cannot be controlled. In addition, these bioreactors simultaneously permit non-destructive observation of cellular behavior and developing vessels, thereby providing one of the key advantages of standard cell culture systems. These bioreactors provide powerful tools for enhancing our precise understanding of the mechanisms of arteriogenesis and vessel formation, and display many of the advantages of current in vitro and in vivo systems 9, 10. In this Bioreactor Core, we will utilize these two novel systems to address specific questions regarding the roles of shear stress and extracellular matrix composition on vessel development.